Contribution of stem cells and differentiated cells to epidermal tumours

The outer covering of the skin-the epidermis-is subject to sustained environmental assaults. As a result, many cells acquire potentially oncogenic mutations. Most cells are lost through differentiation, and only long-term epidermal residents, such as stem cells, accumulate the number of genetic hits that are necessary for tumour development. So, what genetic and environmental factors determine whether a mutant stem cell forms a tumour and what type of tumour will develop?.